The invention relates to a closing device, which more particularly permits the firmly adhering closure of covers or envelopes engaging on packed products and which at one envelope side form an overlap or covering portion. This overlap can e.g. be formed by one or two marginal areas of the envelope engaging over one another in approximately equiplanar manner.
Between the facing or equiplanar engaging sides of the layers to be interconnected there is an adhesive, e.g. in the form of a hot glue. This adhesive is firstly applied to the corresponding side of at least one of the layers in the overlap area, but then has little or a very limited adhesive action in the sense of an adhesive connection the two layers, unless it is activated by special measures diverging from normal climatic conditions, i.e. it is at least briefly transferred in reversible manner e.g. from a solid form into a flowable form. The adhesive can be provided in linear or strip-like manner and in the entire field provided with adhesives in continuous or grid-like form in separate individual fields, e.g. successive adhesion points or strip portions.
For activating the solidified adhesive by liquefication an energy matched to the characteristics of the adhesive and namely by thermal energy in the case of a hot glue is required, which is transferred by radiation and/or conduction through the outer layer of the envelope to the adhesive from a corresponding energy emitter. The surface-specific energy quantity suitable for activating the adhesive is made available in the vicinity of the closing device within an energy field bounded in predetermined manner on the outer circumference. Particularly if said energy field extends up to the outer boundaries of the envelope side of the packed product or projects over said outer boundaries in the direction which is at right angles to the direction in which the envelope layers engage over one another, the adhesive can flow in uncontrolled manner in this direction in a now fluid state. The adhesive can flow beyond the overlap area of the envelope, so that in undesired manner it adhesively connects the inside of the envelope with the pecked product and/or the outside of the envelope with equipment parts and can lead to a significant dirtying effect. The lateral passing out of the activated adhesive from the overlapped area can optionally also take place if the energy field projects in the overlap direction beyond the lateral boundaries thereof.